Mechanical properties of laser welded similar and dissimilar steel joints of TBF1050 and DP1000 steel sheets

Abstract TBF1050 and DP1000 sheets in different thicknesses were laser welded in butt configuration. The welds were performed both similar and dissimilar. Welding speed was changed between 40 and 120 mm/min. Characterization of the welds was carried out by means of microstructure, microhardness, tensile properties and fractography. The grain structure in heat affected zone (HAZ) on DP1000 side was a relatively coarser than that on TBF1050 side. The highest hardness was obtained in fusion zone. The presence of TBF1050 steel in the joint increased the hardness of the fusion zone. On both steel sides, the hardness in a narrow zone between the tempered zone and the base metal decreased below the hardness of the base metals (softening zone). The softening zone hardness on TBF1050 side was relatively higher than that on DP1000 side. The tensile strengths of each laser welded joint, except for DP1000 similar joint, were all higher than 1,000 MPa. When the fractures occurred on the TBF1050 side, the tensile strength was higher. Whether the TBF1050 steel sheet was galvanized or not did not cause any significant effect on the microstructure and the mechanical properties of the joints. The joint fractured from HAZ had a completely brittle fracture behavior.